A simulation optimization model is outlined: traffic signal offsets in intersections are calculated to minimize the travel time of bus users in an urban network. The model considers a passive signal priority system and restricts the maximal incremental delay caused to car users. The simulation tool is able to trace discrete trajectories of both buses and cars in a network. It also evaluates potential perturbations that may cause time variations for average performance. Moreover, the optimization tool is based on evolutionary algorithms. The results of applying the traffic signal coordination model to a set of small trial networks are given. It is proved that the algorithm is able to design a sequence of signal offsets that reduces bus travel times by an 8.5% rate in a real network while maintaining the incremental car delay below 5%.